In the field of medicine, there has been an increasing need to develop implant materials for correction of biological defects. Particularly in the field of orthopedic medicine, there has been the need to replace or correct bone, ligament and tendon defects or injuries. As a result, there have emerged a number of synthetic implant materials, including but not limited to metallic implant materials and devices, devices composed in whole or in part from polymeric substances, as well as allograft, autograft, and xenograft implants. It is generally recognized that for implant materials to be acceptable, they must be pathogen free, and must be biologically acceptable. Generally, it is preferable if the implant materials may be remodeled over time such that autogenous bone replaces the implant materials. This goal is best achieved by utilizing autograft bone from a first site for implantation into a second site. However, use of autograft materials is attended by the significant disadvantage that a second site of morbidity must be created to harvest autograft for implantation into a first diseased or injured site. As a result, allograft and xenograft implants have been given increasing attention in recent years. However, use of such materials has the disadvantage that human allograft materials are frequently low in availability and are high in cost of recovery, treatment and preparation for implantation. By contrast, while xenograft implant materials, such as bovine bone, may be of ready availability, immunological, regulatory and disease transmission considerations imply significant constraints on the ready use of such materials.
In view of the foregoing considerations, it remains the case that there has been a long felt need for increased supplies of biologically acceptable implant materials to replace or correct bone, ligament and tendon defects or injuries. This invention provides a significant advance in the art, and largely meets this need, by providing materials and methods for production of various bone-soft tissue implants from component parts to produce assembled implants.
Orthopedic medicine is increasingly becoming aware of the vast potential and advantages of using bone/tendon/bone grafts to repair common joint injuries, such as Anterior Cruciate Ligament (ACL) or Posterior Cruciate Ligament (PCL) tears. One technique that is currently used for repairing these types of injuries involves surgically reconnecting the torn portions of a damaged ligament. However, this technique is often not possible, especially when the damage to the ligament is extensive. To address situations where the damage to the joint ligaments is severe, another technique commonly performed involves redirecting tendons to provide increased support to a damaged knee. These conventional techniques are not without their shortcomings; in most cases, the repaired joint lacks flexibility and stability.
The recent utilization of bone/tendon grafts has dramatically improved the results of joint repair in cases of severe trauma. Even in cases of extensive damage to the joint ligaments, orthopedic surgeons have been able to achieve 100 percent range of motion and stability using donor bone/tendon grafts. Despite these realized advantages, there have been some difficulties encountered with utilizing bone/tendon grafts. For example, surgical procedures involving transplantation and fixation of these grafts can be tedious and lengthy. Currently, bone-tendon-bone grafts must be specifically shaped for the recipient during surgery, which can require thirty minutes to over an hour of time. Further, surgeons must establish a means of attaching the graft, which also takes up valuable surgery time. Accordingly, there is a need in the art for a system that addresses this and the foregoing concerns. Thus it is an object of this invention to provide a BTB that is constructed to precise dimensions and is adapted for robust fixation while allowing adherence to preferred surgical techniques.
Bone-tendon-bone (BTB) grafts of the prior art are made in one of two ways: (1) by harvesting a naturally occurring tendon/ligament and portions of the bone(s) to which it is attached, thus maintaining the naturally occurring attachment of tendon/ligament and bone; or (2) by attaching the opposing ends of one or more pieces of tendon, ligament or a synthetic material to separate bone blocks. The name BTB is used for historical reasons. One skilled in the art recognizes that by definition, a “tendon” is a collagenous cord that attaches muscle to its point of origin, typically to bone. By definition, a “ligament” is a band of collagenous tissue that connects bone or supports viscera. Thus, it would appear that a BTB would more properly be called a bone-ligament-bone implant. However, many of the earliest BTBs employed a tendon, which is larger and generally more plentiful in a body. Hence, the name BTB became adopted by the art. We have used the term BTB to encompass all of the bone-soft tissue grafts described herein.
Tendons (or ligaments) are fibrous semi-hard materials that are slippery and difficult to grip. Thus, one of the issues in manufacturing an assembled BTB is how to attach the slippery tendon to the bone. The tendon has a tendency to squirm and slip when compressed between boney surfaces, much like a banana peel compressed between the floor and one's foot. One solution that is commonly used is to bite the tendon with a component that has some sort of teeth or threads, providing improved gripping over a flat surface. However, teeth or threads have a tendency to cut into the tendon fibers when the tendon is pulled at high tensile strength. Thus, most assembled BTBs provide some sort of trade-off between reducing slipping and squirming by biting which does not allow for achievement of maximum tensile strength.
U.S. Pat. No. 5,370,662 (“the '662 patent”), which issued to Stone on Dec. 6, 1994 and which is entitled “Suture Anchor Assembly,” discloses the use of a screw made from titanium, stainless steel, or some other durable, non-degradable, biocompatible material having an eyelet at one end for attaching a suture connected to a soft material, such as a ligament or tendon. U.S. Pat. No. 5,370,662 at col. 1, lines 8-9. One problem with such a device is that the screw, although bio-compatible, will never become assimilated into the patient's body. A second problem is that the tendon or ligament will never form a natural attachment to the screw.
One attempt at solving these problems was disclosed in U.S. Pat. No. 5,951,560 (“the '560 patent”), which issued on Sep. 14, 1999 to Simon et al. and which is entitled “Wedge Orthopedic Screw.” The '560 patent discloses a wedge-shaped interference screw made from a biocompatible material for use with a ligament and with two bone blocks for performing anterior cruciate ligament repairs. In the '560 patent, a bio-compatible, wedge-shaped interference screw, a bone block and a ligament are inserted into an osseous tunnel drilled into a bone of a patient in need of a ligament repair. The interference screw compresses the flat surface of a bone block against a ligament that is pressed into the wall of the osseous tunnel. As the interference screw advances, the force that it presses against the ligament is buttressed by the force against the opposing tunnel wall. A second interference screw compresses a second bone block against an opposing end of the ligament in a second osseous tunnel drilled in a second bone in need of ligament repair. It is more difficult to pull a predetermined tension on the tendon because the tendon slips in the bone tunnel and uncontrollably alters the tension when the interference screw is being threaded in the bone tunnel. The slippery ligament is also subject to slippage when compressed between the bone block and the tunnel wall. Such slippage results in a loss of tension in the joint. In the case of an anterior cruciate ligament (ACL) repair, this loss of tension causes a wobbly knee. This is undesirable in any human and particularly athletes. It is an object of the present invention to provide a bone to tendon connection that will decrease slippage and loss of tension in a BTB. Therefore, it is an object of the present invention to provide a BTB with a stiffness of at least 90 N/mm, preferably 170 N/mm, more preferably 230 N/mm. It is also an object of the present invention to provide a BTB with an elongation of no more than 5 mm, preferably less than 2 mm, more preferably less than 1 mm. Stiffness and elongation for any given BTB can be calculated by methods known in the art. Stiffness is defined as the slope of the force-displacement curve when the BTB is subject to axial load increasing from below 100 Newtons to above at least 200 Newtons. Elongation is defined as the difference in length for a given BTB measured before the first cycle of a dynamic load test and after 1000 cycles of loading to at least 200 Newtons.
Another approach to making a BTB is disclosed in U.S. Pat. No. 5,961,520 (“the '520 patent”) which issued to Beck, et al. on Oct. 5, 1999, and which is entitled “Endosteal Anchoring Device for Urging a Ligament Against a Bone.” Like the '560 patent, the '520 patent utilizes an interference screw and a bone block (called an “anchor body” therein) to press the end of a ligament against the side wall of an osseous tunnel in the patient's bone. The '520 patent differs from the '560 patent in that the ligament loops around the bone block in a “U” shape. This “U” shape of the tendon captures the tendon in the first bone tunnel, but leaves two free tendon ends to be secured in the second bone tunnel. In addition in the '520 patent, the bone block, which presses the ligament against the walls of the osseous tunnel contains two grooves for “locking” (col. 7, line 2) the ligament in place, and “restricting excessive compression on the ligament” (col. 7, lines 8-9). The “locking” of the tendon against the tunnel wall still leaves the tendon free to move against the tunnel wall near the ends of the anchor body. This leads to impaired healing and recovery due to tendon to bone contact within the tunnel and also due to micromotions of the tendon within the tunnel. Additionally, the location of the tendon in the locking grooves is a function of the anchor body design and is not a controlled design parameter. Thus, the tendon placement with respect to either the tunnel wall or the tunnel centerline cannot be matched to particular surgical needs or to surgeon preference.
Yet another approach to making a BTB is disclosed in commonly assigned U.S. Pat Appl. Pub. No. 2003/0023304 (“the '304 application”), to Carter et al., which published on Jan. 30, 2003. The '304 application discloses several embodiments of a BTB. In each of the various embodiments, a tendon is bound in an internal chamber created in the bone blocks. For example, in FIG. 10 a plurality of cams reverse the direction of the tendon several times and cancellous chips packed in any open space bite into the tendon to keep it from slipping. In FIG. 12, a screw compresses the tendon against the side of an internal chamber. In FIG. 14, an internal wedge that has teeth bites into a tendon and tightens the grip as the tendon is pulled. In yet another embodiment, shown in FIG. 15, one end of a tendon is doubled over and the doubled over end is held in place by a series of grooves and rings. While all of these embodiments are useful, they each are challenging to manufacture and/or assemble due to their inherent complexity and reliance on small or intricate parts. It is an object of the present invention to provide a BTB having a robust design, simple components, ease of manufacturability, and high reliability, all while maintaining an acceptable tensile strength, stiffness, and elongation performance. This is important for all BTB grafts, especially for those implanted in athletes and other individuals where maximum performance is required.
One isolated and purified BTB that is not hindered by slippage or cut fibers when subjected to high tensile pulling is disclosed in commonly assigned U.S. Pat. No. 6,497,726 (“the '726 patent”) which issued on Dec. 24, 2002 to Carter et al. The '726 patent discloses the use of natural BTBs that are cut from allograft or xenograft sources, commonly referred to as “pre-shaped BTBs.” Typically, the BTB is cut as a single piece from a section of the patella (bone), patellar tendon and the tibia (bone) of the donor. One problem is that only 2-3 grafts can be obtained per knee of the donor, depending upon the donor's age and health. Hence, it is an object of the present invention to be able to make BTB grafts in large quantities. It is also an object of the present invention to make BTB grafts having high tensile strength, suitable for ACL repairs, from tendon and bone components, wherein the BTBs are constructed so as to minimize the art recognized slippage and tearing associated with conventional modes of construction as described above. Another problem with pre-shaped (natural) BTBs is that the size of the BTB or the length of the tendon between the two bone pieces cannot be precisely selected. Some of the physical dimensions of the graft, particularly tendon (ligament) length, are determined by the anatomy of the donor. Frequently, this leads to compromises such as excessive gage length, or length between the bone blocks, which result in surgical challenges and compromised healing and recovery. For example, a natural BTB with a tendon that is too long for an ACL repair results in having a length of unsecured and wobbling tendon in the bone tunnel between the ends of the secured bone portions. The wobbling tendon hinders healing in the bone tunnel. Hence, it is yet another object of the present invention to be able to make BTB grafts having a predetermined and variable set of design parameters including gage length, bone block diameter, tendon size, and bone block or tendon shape, size, orientation or a combination thereof.